The present invention relates to surfactants. More particularly, the present invention relates to fish proteins which can be used as surfactants.
Surfactants are used as dispersants, emulsifiers, foaming agents, wetting agents, and spreading agents. Surfactants are amphipathic molecules. The word amphipathic comes from the Greek, amphi meaning dual and Pathos meaning suffering. Thus an amphipatic molecule is a molecule which "suffers" both oil and water phases. Amphipathic molecules consist of a hydrophobic portion and a hydrophilic portion; typical examples are stearic acid and lauryl alcohol. Surfactants are used as wetting and spreading agents in commercial applications such as enhanced oil recovery, dispersion of powders in liquids, application of agricultural sprays and cosmetics.
The term wetting is often used loosely, but in fact there are three distinct types of wetting, designated adhesional wetting, spreading wetting, and immersional wetting. These may be better understood by considering the stages involved in immersing a solid cube, of side 1 cm, into a liquid.
Adhesional wetting occurs when the first face of the cube comes into contact with the liquid surface. The isothermal work associated with this process if given by EQU Wa=.gamma..sub.s/l -(.gamma..sub.s/v +.gamma..sub.l/v) (1)
where .gamma..sub.s/l, .gamma..sub.s/v and .gamma..sub.l/v are the interfacial free energies associated with the solid/liquid, solid/vapor and liquid/vapor interfaces respectively, and Wa is the work of adhesion of the liquid to the solid.
Immersional wetting occurs as the sides of the cube become submerged. As this happens, the solid vapor interface is directly exchanged for an equivalent area of solid/liquid interface. In this case: EQU Wi=.gamma..sub.s/l -.gamma..sub.s/v (2)
Spreading wetting takes place when a drop of liquid spreads over a plane solid surface such as when the top surface of the cube is submerged. When this happens a solid/vapor interface is replaced by equal areas of solid/liquid and liquid/vapor interfaces.
The work of spreading, therefore, can be equated to the relevant interfacial free energies: EQU Ws=(.gamma..sub.s/l +.gamma..sub.l/v)=.gamma..sub.s/v (3)
Values of .gamma..sub.s/v and .gamma..sub.s/l are not readily accessible by experiment, but they are related by the Young-Dupre equation for contact-angle of a liquid drop on a solid surface measured through the liquid. The Young-Dupre equation is EQU .gamma..sub.s/v =.gamma..sub.s/l +.gamma..sub.l/v cos.theta.(4)
Substituting equation (4) into equations (1), (2), and (3) gives EQU Wa=.gamma..sub.s/l -(.gamma..sub.l/v +.gamma..sub.s/v)=-.gamma..sub.l/v (cos.theta.+1) (5) EQU Wi=.gamma..sub.s/l -.gamma..sub.s/v =.gamma..sub.lv cos.theta.(6) EQU Ws+(.gamma..sub.s/l +.gamma..sub.l/v)-.gamma..sub.s/v -.gamma..sub.s/v =-.gamma..sub.l/v (cos.theta.-1) (7)
For a spontaneous process to occur, W must be negative. Therefore:
(i) Adhesional wetting occurs (Wa is negative) regardless of the value of cos.theta.. That is, adhesional wetting is always spontaneous. PA1 (ii) Spreading wetting occurs only when cos.theta.=1. That is, when .theta.=0.degree.. PA1 (iii) Immersional wetting occurs and immersion is spontaneous when .theta. lies between 0.degree. and 90.degree..
When an aggregate is introduced to a liquid, if the contact-angle of the liquid on the solid is less than 90.degree., the spontaneous immersional wetting will occur. In order to decrease the aggregate size without exerting an inordinate amount of mechanical shear, however, the liquid must penetrate the pore structure of the aggregate and this can be achieved only by spreading wetting, with a contact-angle of 0.
Factors which are important in forcing liquid into the channels between and inside agglomerates cannot be precisely defined, but the important parameters can be elucidated by considering the pressure (P) required to force liquid into a capillary of radius, r: EQU P=-2.gamma..sub.l/v cos.theta./r (8)
Substituting from equation (4) EQU P=-2(.gamma..sub.s/v -.gamma..sub.s/l)/r (9)
Therefore, for penetration to proceed .gamma..sub.s/l should be made as small as possible. If the liquid spreads into the pores, then, from equation (6), .theta. should be zero. However, if .theta. is zero, equation (8) becomes EQU P=-2.gamma..sub.l/v /r (10)
Therefore, for penetration to occur .gamma..sub.l/v should be as large as possible. However, most surfactants lower both .gamma..sub.l/v and .gamma..sub.s/l simultaneously. The rate of penetration is also an important factor. This rate is defined by the Washburn equation, which for a packed bed of porous particles becomes ##EQU1## where 1 is a depth of penetration in time t, .eta. is the liquid viscosity, and K is a factor which defines the equivalent "capillarity" of the bed.
Equation (11), therefore, tells us that for fastest penetration, sufficient surfactant should be added to decrease the contact-angle, .theta., to zero. Addition of further surfactant will reduce .gamma..sub.l/v while cos.theta. will remain at unity. This means that adding excess surfactant will actually reduce the rate of penetration of the liquid into the pores.
Surfactants are generally divided into four classes: amphoteric, with zwitterionic head groups; anionic, with negatively charged head groups; cationic, with positively charged head groups; and nonionic, with uncharged hydrophilic head groups. Anionic surfactants include long-chain fatty acids, sulfosuccinates, alkyl sulfates, phosphates, and sulfonates. Cationic surfactants include protonated long-chain amines and long-chain quaternary ammonium compounds. Amphoteric surfactants include betaines and certain lecithins. Nonionic surfactants include polyethylene oxide, alcohols, and other polar groups.
Because of their many uses and potential uses, it would be an advancement in the art to provide a novel source of surfactants that could be produced economically. It would be a further advancement if those surfactants had unique properties. Such surfactants are disclosed and claimed herein.